1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus, and more particularly, to a fusing device having improved performance and compactness, and an image forming apparatus having the same.
2. Description of the Related Art
In general, an image forming apparatus refers to an apparatus that forms an image on a printing medium, in accordance with input image signals. For example, a printer, a photocopier, a facsimile, and a multifunction peripheral (MFP) having combined functions of the aforementioned apparatuses, are examples of image forming apparatuses.
An electrophotographic image forming apparatus forms a desired image in the following process. First, a surface of a photoconductive medium is electrified to a predetermined electric potential. A laser beam is projected onto the surface of the photoconductive medium, to thereby form an electrostatic latent image. A toner image is obtained, by applying toner to the electrostatic latent image. Next, the toner image is transferred to a recording medium, and then fixed on the recording medium, by passing through a fusing device.
A fusing device generally comprises a heating roller including a heat source therein, and a pressing roller to form a fusing nip, through contact with the heating roller. As a printing medium, having a transferred toner image, is passed between the heating roller and the pressing roller, the toner image is fixed on the printing medium, by heat transmitted from the inside of the heating roller, and pressure between the heating roller and the pressing roller.
Currently, the tendency is toward high-speed and compact image forming apparatuses. Accordingly, fusing devices that have improved performance and a reduced size, are sought after.
Since the performance of a fusing device depends on the width of a fusing nip, it is preferable to enlarge a diameter of the pressing roller, to produce a higher performance fusing device. However, in this case, a diameter of the heating roller has to be accordingly enlarged, thereby increasing the size of the fusing device.
Considering such problems, a fusing device employing a pair of relatively small pressing rollers has been introduced, as shown in FIG. 1. The fusing device comprises a heating roller 1 including a heat source 1a, and first and second pressing rollers 2 and 3 disposed along a feeding direction of a printing medium M, and tightly contacting the heating roller 1. The first pressing roller 2 is biased toward the heating roller 1, by a first compression spring 4 mounted on the opposite side to the heating roller 1. The second pressing roller 3 is biased toward the heating roller 1, by a second compression spring 5. The use of the two pressing rollers 2 and 3 produces two fusing nips, which thereby increase a total nip area, resulting in the fusing device having improved fusing performance, while keeping a compact size.
In the fusing device shown in FIG. 1, however, the first compression spring 4 is mounted to the opposite side to the heating roller 1, to push the first pressing roller 2 toward the heating roller 1. In such a structure, the height of the fusing device should be increased, in order to secure a mounting space 6 for the first compression spring 4. This increases the size of the image forming apparatus.
Besides the performance improvement and the size reduction, a transfer path, along which the printing medium is transferred, is also a consideration. The printing medium can be curled as it passes through the fusing device. Without proper guidance, the curled printing medium may be jammed inside the fusing device, which can result in loss of image quality.